The present invention relates to a self-centering support for clamping and/or supporting a workpiece on a turning lathe with three securing members connected in the housing and adjustable in a common plane for securing the workpiece, wherein the two laterally positioned securing members are mirror-symmetrically arranged relative to one another and are pivotably supported on pivot bolts at the housing. They are embodied as angular levers and the centrally positioned securing member is radially slidably guided toward the workpiece within the housing and actuatable by an actuating piston loaded by a pressure medium. The centrally positioned securing member has a center piece that is provided with control surfaces and that cooperates with free ends of the angular levers, preferably via rollers. For increasing the insertion opening of the support, one or two of the laterally positioned securing members are coupled with a rocker arm to the center piece or the centrally positioned securing member for a forcible displacement.
From German Patent 35 43 806 a support of the aforementioned kind is known which has been successfully used in practice. In this known design, one of the two laterally positioned securing members is pivotable for enlarging the insertion opening due to an additional displacement movement of the centrally positioned securing member and the rocker arm which is directly connected to the center piece. However, due to the connection of the rocker arm at the center piece the pivoting range is limited. The rocker arm in this design is connected between the pivot bolt supporting the securing member and the roller connected to the securing member and cooperating with the control surface of the center piece. Furthermore, it is disadvantageous that a spring is supported at the rocker arm which, for compensation of different displacement strokes of the securing member, is provided with a slotted hole that is engaged by a bolt connected to the securing member. When the spring breaks, respectively, when the prestress decreases, a guiding of the outer securing member is no longer provided.
It is therefore an object of the present invention to provide a self-centering support of the aforementioned kind with which at least one of the two laterally positioned securing members can be outwardly pivoted by an additional displacement movement of the centrally positioned securing member and with which a secure coupling of the additionally pivotable securing member is ensured. The laterally positioned securing member should be pivotable about 90.degree. and more relative to the clamping position so that even for a vertical arrangement of the support the workpieces to be machined can be horizontally inserted. The required constructive expenditure should be minimal; however, it should be ensured that even for high loads damages are prevented and a high operational safety is attainable. It should furthermore be possible that a securing member which is not additionally adjustable can be supported in any suitable angular position.